1. Field of the Invention
The invention relates to a positive photoresist composition and method of pattern forming using the same. More particularly, the present invention relates to a positive photoresist composition with uniform reactivity and method of pattern forming using the same.
2. Description of the Related Art
As semiconductor devices are scaled down, lithography is required for achieving higher integration with device design. To conform to various electronics and optoelectronics requirements, circuit board technology is evolving toward high density interconnection (HDI), fine pitch, and high aspect ratio.
Thick film photolithography employing negative photoresists has been widely used in semiconductor fabrication. Typical resolution can range from 10˜50 μm lines and spaces at a film thickness of 10˜50 μm range. The circuit board requires a greater number of layers to accommodate the longer circuit and increased number of I/O points. Moreover, as electronic products become thinner and smaller, high density interconnection (HDI) substrates are the primary method of reducing manufacturing cost while maintaining the desired product size. Thus, thick film photoresist resolution must be approached to at least 10˜25 μm. Due to the low resolution, however, the application of thick film photolithography employing negative photoresists is limited.
Theoretically, the use of positive photoresist can facilitate forming a thick photoresist pattern with high resolution in the photolithography process, thereby reducing defects for subsequent a via hole pattern formation, in comparison with negative photoresist. In general, the conventional positive photoresist compositions can be classified as either diazonaphthoquinone-novolac (DNQ/Novolac) type resists (non-chemically amplified type resists) or chemically amplified type resists depending on the exposure source thereof. The DNQ/Novolac positive photoresists, however, have an optimum resolution of 0.35˜5 μm with 0.5˜5 μm thickness, and the chemically amplified positive photoresists have an optimum resolution of 0.3˜0.09 μm with 0.2˜0.5 μm thickness.
When a conventional positive photoresist composition is employed in a thick film lithographic process, exposure of the photoresist layer poses the problem of transmittance degradation caused by absorption in the photoresist, due to a thickness of the photoresist layer being more than 5 μm. The difference of exposure dose between the top and bottom of the photoresist layer would be huge, such that residual materiel on the bottom of the photoresist layer is difficult to remove after development. The residual photoresist creates uneven surfaces due to defects such as distortion, swelling or raising, resulting from incomplete reaction of photoresist composition. Hence, the photolithography resolution of the positive photoresist is limited.
A chemically amplified resin reacts with acid molecules generated by a photoacid generator after exposure to irradiate and catalytically deprotect acid labile groups of the chemically amplifyed resin. During deprotection, the exposed chemically amplifyed resin releases H+ which facilitates the deprotection and further reduces activation energy required of the photoacid generator. Accordingly, chemically amplified resin is often employed by positive photoresist for high sensitivity and lowering the exposure energy. However, the obtained chemically amplified photoresist pattern has a low photoresist contrast resulting in uneven profiles, due to inferior dissolution inhibition and reaction uniformity of chemically amplified resin.
As electronic products become thinner and smaller, high density interconnection (HDI) substrates are the primary method of reducing manufacturing cost while maintaining the desired product size. Thus, thick film photoresist resolution must be approached to at least 10˜25 μm. Therefore, developing a simple photoresist technology offering a complete figure, high aspect ratio, and superior resolution is necessary.